Enantiodiscrimination in NMR spectra and X-ray structures of diastereomeric salts of trans-4-(4-fluorophenyl)-3-hydroxymethyl-1-methylpiperidine with (S)-Mosher acid
| Authors | |
|---|---|
| Year of publication | 2002 |
| Type | Article in Periodical |
| Magazine / Source | J. Chem. Soc. Perkin Trans. 2 |
| MU Faculty or unit | |
| Citation | |
| Field | Organic chemistry |
| Keywords | enantiodiscrimination; (S)-Mosher acid; NMR; diastereomeric salts;free energy; |
| Description | Signal anisochrony delta in NMR spectra of racemic trans-4-(4-fluorophenyl)-3-hydroxymethyl-1-methylpiperidine 1 induced on the formation of diastereomeric salt complexes with (S)-Mosher acid 2 showed a strong dependence on solvent polarity, concentration, stoichiometric ratio and enantiomeric composition. X-ray structures of the salts, 3a and 3b, revealed that the conformations of the protonated base in ion pairs are very similar with respect to interatomic distances, bond and torsion angles but the mutual orientation of counterions in ion pairs differs significantly. It is suggested that the conformations of transient diastereomeric complexes in solution, responsible for delta;, resemble those in solid state. Furthermore, ab initio calculations performed on the optimized X-ray geometries of both ion pairs showed that the free energy of 3a is lower than that of 3b. This implies that the association constant for the formation of 3a is higher than that of 3b. |
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